Narrow-band transmission spectroscopy of HD 189733b with UVES
Narrow-band transmission spectroscopy of HD 189733b with UVES
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使用 UVES 对 HD 189733b 进行窄带透射光谱分析
DOI：
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发表时间：
2018
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通讯作者：
R. Collet
中科院分区：
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作者：
S. Khalafinejad;C. V. Essen;H. J. Hoeijmakers;G. Zhou;T. Klocova;J. H. M. M. Schmitt;S. Dreizler;M. López;T. Husser;T. O. B. Schmidt;R. Collet
上下文在主凌日期间，可以使用透射光谱学测量系外行星大气的光谱特征。我们可以通过研究系外行星在光学区域的过量钠吸收来获得这些行星高层大气的信息。然而，许多因素会影响观察到的钠吸收特征。我们提出了一个详细的模型校正系统偏差，以产生一个准确的深度在HD 189733b的钠吸收。目标。这项工作的目标是精确测量HD 189733b的大气钠吸收光变曲线，校正恒星边缘变暗、恒星活动和系外行星径向速度变化引起的“碰撞”的影响。事实上，由于我们数据的高节奏和高质量，这是第一次可以通过视觉检查检测到最后一个特征。方法.我们使用安装在VLT的UVES仪器拍摄的244个高分辨率光谱。我们的观测涵盖了HD 189733b的一次完整凌日，其步频为45秒。为了探测钠的透射光谱，我们在每个钠D线的核心内，在1 μ m、1.5 μ m和3 μ m的通带内，产生了对恒星通量积分的过量光变曲线。我们模拟外部源的影响，多余的光变曲线，这对应于所观察到的恒星耀斑开始接近中期过境时间和波长依赖的边缘变暗的影响。此外，通过表征恒星钠线内行星钠线的径向速度变化和多普勒频移的影响，我们估计了系外行星钠特征的深度和宽度。结果我们通过等效宽度为0.0023 ± 0.0010 μ m的高斯分布估计了行星钠线的形状，从而证实了HD 189733 b大气中钠的存在，对于1 μ m，1.5 μ m，3、分别。使用行星钠线的等效宽度，我们产生一阶估计的数密度的钠在系外行星大气。
Context. During primary transits, the spectral signatures of exoplanet atmospheres can be measured using transmission spectroscopy. We can obtain information on the upper atmosphere of these planets by investigating the exoplanets’ excess sodium absorption in the optical region. However, a number of factors can affect the observed sodium absorption signature. We present a detailed model correcting for systematic biases to yield an accurate depth for the sodium absorption in HD 189733b. Aims. The goal of this work is to accurately measure the atomspheric sodium absorption light curve in HD 189733b, correcting for the effects of stellar differential limb-darkening, stellar activity, and a “bump” caused by the changing radial velocity of the exoplanet. In fact, owing to the high cadence and quality of our data, it is the first time that the last feature can be detected even by visual inspection. Methods. We use 244 high-resolution optical spectra taken by the UVES instrument mounted at the VLT. Our observations cover a full transit of HD 189733b, with a cadence of 45 s. To probe the transmission spectrum of sodium we produce excess light curves integrating the stellar flux in passbands of 1 Å, 1.5 Å, and 3 Å inside the core of each sodium D-line. We model the effects of external sources on the excess light curves, which correspond to an observed stellar flare beginning close to mid-transit time and the wavelength dependent limb-darkening effects. In addition, by characterizing the effect of the changing radial velocity and Doppler shifts of the planetary sodium lines inside the stellar sodium lines, we estimate the depth and width of the exoplanetary sodium feature. Results. We estimate the shape of the planetary sodium line by a Gaussian profile with an equivalent width of ∼0.0023 ± 0.0010 Å, thereby confirming the presence of sodium in the atmosphere of HD 189733b with excess absorption levels of 0.72± 0.25%, 0.34± 0.11%, and 0.20± 0.06% for the integration bands of 1 Å, 1.5 Å, and 3 Å, respectively. Using the equivalent width of the planetary sodium line, we produce a first order estimate of the number density of sodium in the exoplanet atmosphere.